Fluid pressure pump apparatus and method using the same



L. T. RYAN FLUID PRESSURE PUMP APPARATUS AND METHOD USING THE SAME 13,

Sheet of 5 Filed May Luau/aw 7 EP44/ Feb. 18, 1969 Filed y 15. 1966 1.. T. RYAN 3,427,749 FLUID PRESSURE PUMP APPARATUS AND METHOD USING THE SAME Sheet 2 of I J8 Ii 23 I k I l l i ii 3 25 431 FIEZ INVENTOR. 44430241 7. 21 441 Arrow/1 Feb. 18, 196 9 3,427,749

ID PRESSURE PUMP APPARATUS AND METHOD USING TH L. T. RYAN FLU E SAME Sheet Filed May 15, 1966 INVENTOR.

L/LBl/Bil ha /W United States Patent Office 3,427,749 Patented Feb. 18, 1969 3,427,749 FLUID PRESSURE PUMP APPARATUS AND METHOD USING THE SAME Lilburn T. Ryan, Houston, Tex., assignor to G. H. Tennant Company, Minneapolis, Minn. Filed May 13, 1966, Ser. No. 549,889 US. C]. 51-12 Claims Int. Cl. B24c 3/00 ABSTRACT OF THE DISCLOSURE A method and apparatus of entraining and discharging a fiowable abrastive material into a stream of air under pressure which includes introducing fiowable abrasive material alternately into one and then another of a pair of pressure chambers, while the pressure chambers are in an unpressurized condition. Pressurizing each loaded pressure chamber and then intercommunicating the loaded pressurized chamber with a collection chamber to permit the abrasive material to flow into the latter. Each pressure chamber being alternately filled with abrasive material and then evacuated so that the collection chamber is continuously supplied with abrasive material. Continuously discharging the fiowable abrasive material from the collection chamber and entraining the abrasive material in a rapidly moving stream of air under pressure.

In some of the conventional abrasive blasting systems which have been developed for the purpose of treating or cleaning surfaces, the fiowable abrasive, such as sand, is entrained in a stream of air under pressure and is directed against the surface to be cleaned at extremely high velocities. In many of these conventional abrasive blasting systems, the container for the fiowable abrasive material actually constitutes a pressurized vessel and this type of abrasive blasting system is therefore quite heavy and bulky. Movement of this kind of equipment from one location to another involves a time consuming and tedious operation. It is also pointed out that there are no heretofore known continuously operable abrasive blasting systems, although prior art attempts have been made to develop such a continuously operable apparatus. Although some abrasive blasting apparatus have only a relatively short period of interruption, this interruption of the air entrained stream of material does, in fact, disturb the uniformity of the stream as it is applied against the surface being treated, which is a condition that is undesirable.

It is therefore, a general object of the present invention to provide a high capacity method and apparatus, of simple and inexpensive construction, for continuously entraining a fiowable material, such as abrasives and the like, in a stream of air under pressure for use in sandblasting operations, so that interruptions in the sandblasting operation for the purpose of reloading are avoided.

Another object of this invention is to provide a lightweight material supplying apparatus which is capable of very effectively entraining the particulate material such as an abrasive into a stream of air for use in a surface treating operation, and which, because of its lightweight construction and relatively small compass, thereby lends itself to greater portability.

These and other objects and advantages of this invention will more fully appear from the following description made in connection with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views, and in which:

FIG. 1 is a perspective view of the fluid material supplying apparatus;

FIG. 2 is a cross-sectional view on an enlarged scale of the apparatus;

FIG. 3 is a detail sectional view of a valve device utilized in the apparatus; and

FIG. 4 is a schematic flow diagram of the apparatus.

Referring now to the drawings, and more specifically to FIGS. 1 and 2, it will be seen that one embodiment of the fluid materials supplying apparatus, designated generally by the reference numeral 10 is there shown. It is pointed out, that the material supplying apparatus 10 is contemplated for use in a surface treating system such as an abrasive blasting operation. The apparatus 10 includes a supporting frame 11, constructed of suitable rigid vertical and horizontal frame elements, the frame serving to support the apparatus upon any suitable supporting surface. The apparatus also includes an open top container or hopper 12 having peripheral walls which converge downwardly from adjacent the mid-portion of the hopper. These upstanding peripheral walls are rigidly secured to the bottom wall or floor 13 of the hopper and bottom wall 13 has a pair of spaced apart openings 14 therein which communicate with the pump device 15.

The pump device 15 includes a pair of similar pump bodies or housings 16 each being constructed of a rigid metallic material and being designed to withstand substantial fluid pressures. It will be noted, that each of the pump housings 16 includes a neck 17 which projects upwardly therefrom and which has an annular attachment plate 18 secured to the upper end thereof for attachment to the bottom wall of the hopper.

The neck 17 of each of the pump housings 16 has a funnel shaped material directing member 19 positioned interiorly thereof and the lower inner peripheral surface of this funnel-shaped member has an annular groove 20 therethin in which is positioned an annular sealing or O-ring element 21. The O-ring element 21 is preferably formed of a somewhat yieldable compressible material such as rubber or the like, and defines a valve seat, the specific function of which will be described more fully hereinbelow.

An elongate generally vertically oriented valve support cage 22 is secured to the funnel-shaped member 19 and projects downwardly through the pump housing 16. The valve support frame 22 is comprised of a plurality of vertical support elements 23, preferably arranged in cylin- I drical fashion and rigidly interconnected at their respective end to annular end frame elements 24. It will be noted, that the lower end portion 25 of each of the pump housings 16 is of generally cylindrical configuration as best seen in FIG. 3.

It will be seen that the cylindrical lower end portion 25 of each housing 16 has an annular member 26 disposed concentrically therein and secured thereto, and this annular member 26 has a downwardly converging generally frusto-conical material directing surface 27. The annular member 26 also has an inwardly facing annular groove 28 therein and O-ring 29 formed of a somewhat yieldable resilient material such as rubber or the like is positioned in this annular groove as best seen in FIG. 3. The O-ring element 29 also serves as a valve seat in a manner to be described more fully hereinbelow.

It will be noted, that the lower end portion of the valve support cage 22 is secured to the annular member 26. An annular filter structure 30 extends between the inner surface of the pump housing neck 17 and the exterior surface of the valve support cage 22, so that an annular air inlet chamber 31 is defined therebetween. The filter structure 30 includes a rigid generally hollow annular member having perforations therein and also having suitable filter material such as steel wool interposed therein to filter foreign material from the air as it is introduced into the annular chamber 31. To this end, it will be noted that the neck 17 of each of the pump housings 16 has an inlet fitting 32 secured thereto which communicates with the annular chamber 31 so that air under pressure introduced through the inlet fitting passes into the annular chamber 31 and thereafter downwardly through the filter 30, and into the interior 16a of the associated pump housing 16.

A relatively small, substantially rigid conduit 32a is positioned in the pump housing 16 and has its upper end projecting through the filter structure 30 and communicating with the annular chamber 31. The other end portion of the conduit 32a is connected in communicating relation to a pump housing or cylinder 33, the latter being rigidly afiixed to the valve support cage 22 by suitable spider elements 34. The interior of the valve cylinder 33 defines a chamber 35 and an upper piston element 36 and a lower piston element 37 are positioned in the valve cylinder for axial movement relative thereto. Each of the pistons 36 and 37 has a bore therethrough and it will be seen that a valve stem 38 is positioned in the bore of the upper piston 36 and is secured thereto by pin 38a. Similarly, a valve stem 39 is projected to the bore of the lower piston element 37 and is secured thereto by suitable securing pin 39a.

A poppet valve element 40 is secured to the upper valve stem 38 while a similar shaped poppet valve element 41 is secured to the lower valve stem 39. It will be noted, that these poppet valve elements are of semi-hemispherical shape and each is preferably constructed of a slightly yieldable abrasion resistant material such as rubber. The convex surface of each upper poppet valve element 40 faces upwardly and engages the O-ring element 21 when this poppet valve element is moved to close communication between the hopper 12 and the pump housing 16. Similarly, the poppet valve element 41 also has its convex surface facing upwardly which is engageable with the O-ring element 29 as shownin FIG. 3, when the poppet element is in its closed condition. An elongate helical coil spring 41a has its opposite end portions projecting into the respective bores of the pistons and these end portions are attached to the pistons. Therefore, axial movement of the pistons away from each other is resisted by the spring 41a. It will be seen, that when air under pressure is introduced into the chamber 35 through the conduit 32a, the air pressure will urge the upper and lower piston elements away from each other, so that the upper valve element will be moved into seated relation against the O-ring element 21, which actually defines a valve seat and the co-aeting yieldable surface will serve to sealingly close the hopper from the pump housing 16. Simultaneously, during this movement, the lower valve element 41 will be moved away from seated relation with respect to the O-ring element 29 to open the lower end portion of the pump housing. It will be seen, that the helical spring 41a tends to resist axial movement of the piston elements away from each other so that in the unpressurized condition, the upper valve element will be urged to an open condition with respect to the hopper 12, while the lower valve element 41 will be urged to its closed condition.

Referring again to FIG. 2, it will be seen that the pump device also includes a gathering chamber housing 42, which is rigidly secured to the pump housings 16. This gathering chamber housing 42 includes an upper portion 43 which is that portion of the gathering chamber housing which is rigidly affixed to the pump housing 16 so that at least a portion of the pump housings project interiorly of the gathering chamber housing 42. The gathering chamber housing 42 also includes a lower portion 44, which is secured to the top portion by nut and bolts assembly 45 that project through apertured outturned flanges respectively affixed to the upper and lower portions of the gathering chamber housing. It will be seen, that the lower cylindrical end portion of each pump housing communicates with the interior 46 of the gathering chamber housing 42, whereby when the lower valve elements 41 of each pump housing is shifted to the open condition, the mixture of abrasive and air within the pump housing 16 will flow downwardly into the gathering chamber interior 46.

The lower end portion 47 of the gathering chamber housing 42 is of cylindrical configuration and is internally threaded for attachment to an externally threaded nipple 48. The upper internally threaded end 49 of a metering valve mechanism 50 threadingly engages the nipple 48 so that the metering valve is suspended from the gathering chamber housing, and intercommunicates with the interior of the latter. This metering valve mechanism 50 is variably adjustable to permit selective volume control of the air entrained abrasives, such as sand, being discharged from the valve mechanism. 'It is felt, that specific details of construction of this metering valve mechanism need not be set forth in the instant application, since this mechanism per se does not constitute part of the present invention.

Air under pressure is supplied from an air compressor 51 to a four-way control spool valve 52 through a conduit 53. A suitable shut-off valve 54 is interposed in flow controlling relation in the conduit 53 so that the volume of air to the control valve may be selectively controlled. The four-way control spool valve 52 has a pair of outlet ports each of which is connected to one of a pair of conduits 55. These conduits 55 have their respective other ends connected to the fittings 32, shown in FIG. 3, each of which are mounted in a pump housing 16. The fourway control spool valve 52 therefore serves to alternately supply air under pressure to the pump housings 16.

The means for controlling operation of the four-way spool valve 52 comprises a double acting pneumatic cylinder 56 having a piston which is connected to a piston rod 57. Opposite end portions of the pneumatic cylinder 56 are connected in communicating relation to the pump housings 16 through conduits 58, so that when air under pressure is supplied to one of the pump housings, air will also be supplied through the associated conduit 58 to one end portion of the pneumatic cylinder 56 to move the piston axially therein. Similarly, when air is applied under pressure to the other pump housing, air will also be supplied through the associated conduit 58 to the other end of the pneumatic cylinder 56 to shift the piston therein and the rod 57 carried thereby in the opposite direction.

The four-way spool valve 52 has a pair of spring loaded bleed-off valves 59 disposed in controlling relation with respect to a pair of outlet ports associated therewith. It will be noted, that one of the bleed-off valves 59 is connected by conduit 60 to its associated bleed port and is therefore remotely located with respect to the spool valve body. These spring loaded bleed-off valves are normally closed and are opened when engaged by an actuating arm 61 carried by the piston rod 57. Thus, when the piston rod 57 is extended with respect to the pneumatic housing 56 the rod will engage and open that bleed-off valve which is remotely located with respect to the spool valve housing. Retraction of the piston rod 57, on the other hand, will cause the actuating arm 61 to move out of engagement with respect to the remotely located bleed-off valve 59 thus permitting the same to be closed and the actuating arm will engage and open the other bleed-off valve.

Opening and closing of the bleed-off valves 59 cause shifting of the spool (not shown) in the four-way valve, so that either one or the other of the pump chambers 16 will be intercommunicated with the main pressure conduit 53 through its conduit 55 by intereommunicating inlet and outlet ports in the valve structure. Thus, when one of the bleed-off valves 59 is depressed and thereby opened, the main pressure conduit 53 will be intercommunicated with inlet conduit 55 for one of the pump housings 16, while the reverse condition is true when the other bleed-off valve is actuated and opened.

The four-way spool valve 52 also has a pair of exhaust ports 62, one of which is intercommunicated with one of the conduits 55 when the pump housing 16 associated therewith is not connected in communicating relation with the main pressure conduit 53. Therefore, when one of the pump housings 16 is being pressurized, the air pressure in the other of the pump housings will be exhausted through its associated exhaust port 62 in the four-way control spool valve 52.

One end of a conduit 63 is connected in communicating relation to the main supply or pressure conduit 53, and the other end of this conduit is connected in communicating relation to the gathering chamber housing 42. A suitable pressure regulator valve 64 is interposed in flow controlling relation with respect to the conduit 63 so that the pressure to the gathering chamber housing may be selectively adjusted. Thus air under pressure during normal operation of the apparatus is normally supplied to the gathering chamber housing 42.

The metering valve mechanism 50 is also connected to the main pressure conduit 53 by means of a conduit 65, so that the metering valve mechanism is also supplied with a stream of air during normal operation of the apparatus. A suitable choke valve mechanism 66 is interposed in flow controlling relation with respect to the conduit 65 to permit the supply of air to the metering valve 50 to be regulated. The metering valve mechanism is also provided with an outlet which is connected in communicating relation to an elongated discharge conduit 6511, the latter being provided with a nozzle mechanism (not shown) at its other end through which the material is discharged against the surface to be treated.

Although the pneumatic cylinder 56 is only diagrammatically illustrated, it is pointed out that the pneumatic cylinder is provided with a pair of flow control regulators 56a, each being disposed adjacent one end of the cylinder and being adjustable to control the flow of air out of each cylinder and into one of the pump chambers 16. With this arrangement, by regulating the flow of air out of the air cylinder 56 the rate of movement of the piston and piston rod 57 may be adjusted. By adjusting the rate of movement of the piston rod 57, the time required to alternate the pressurizing and exhausting cycle of each pump chamber may be varied to thereby permit the amount of abrasives introduced into the pump chambers to be variably adjusted during the operation of the apparatus.

During operation of the apparatus 10, the hopper 12 will be provided with a supply of abrasives, such as sand, and this sand will be alternately introduced into each pump housing 16. For exemplary purposes, it will be assumed that the pump housing 16 located at the left as viewed in FIG. 2 will be charged or loaded with a supply of suitable flowable abrasive from the hopper 12 and in order for this condition to occur it will be noted that the upper valve element 40 of the left pump housing is disposed out of closing relation with respect to its valve seat, and the associated lower valve element 41 will be moved into its closed condition with respect to its valve seat. Since this pump chamber located at the left is being loaded with the abrasive from the hopper 12, the'interior of this pump chamber will communicate with the exterior and therefore will be at atmospheric pressure. As this is occurring, air under pressure is being supplied through conduit 53 from the compressor 51 into the pump housing 16 located at the right of FIG. 2 and air is also being directed into the air cylinder 56 from the pump housing 16 being pressurized through the conduit 58 to thereby cause retraction of the piston rod 57.

Since the gathering chamber housing 42 is also being supplied with air under pressure, and since the pump housing 16 located at the left of FIG. 2, which is being loaded with sand, is at atmospheric pressure, the pressure within the gathering chamber housing is greater than the air pressure within that pump housing being charged with the abrasive so that the lower valve element 41 of the last-mentioned pump housing will be held in the closed condition. The spring 41a in associated pump housing 16 also assists in holding the associated valve element in the closed position. Further, since air under pressure is being supplied to the pump housing 16 located at the right, the air pressure being introduced therein and through the conduit 32a will urge the upper valve element into closed relation with respect to the hopper 12 and prevent the flow of abrasive therein. However, the air pressure in the gathering chamber 42 is greater than the air pressure in the pump chamber 16 being pressurized so that the lower valve elements 41 associated therewith will also be held in a closed condition.

The pump chamber at the right as viewed in FIG. 2, will contain a predetermined amount of sand or other abrasive therein and when the air pressure in this pump chamber exceeds that in the gathering chamber 46, the lower valve element 41 will be shifted downwardly so that the air and sand will flow into the gathering chamber by action of gravity and air pressure. This mixture of abrasive and air will thereafter flow downwardly from the gathering chamber through the nipple 48 and into the metering valve 50. The stream of air introduced into the metering valve 50 through the conduit will entrain the abrasive therein and will pass outwardly through the outlet opening in the metering valve and into the discharge conduit 65a associated therewith. As pointed out above, the choke valve mechanism 66 may be regulated to control the flow of air into the metering valve through the conduit 65.

By adjusting the adjustable flow regulator 56a, the loading and exhausting or emptying cycles of the pump housing 16 may be readily adjusted. Thus adjustment of these flow control regulators may be set so that the time required to fill one pump housing 16 corresponds to that time required to empty the other pump housing.

It will be seen, that as the pump housing 16 located at the right as viewed in FIG. 2 is being emptied of its mixture of abrasive and air into the gathering chamber, the piston rod 57 and the actuating arm carried thereby will be moving in a direction toward the bleed-off valve 59 which permits movement of the spool in the spool valve 52 in a direction to shut-off air under pressure to the pump housing located at the right. Therefore, when the actuating arm 61 engages this last mentioned bleedoff valve, the spool in the spool valve 52 will be shifted and air will be exhausted from the pump housing 16 located at the right while air under pressure will then be supplied to the pump housing located at the left as vlewed in FIG. 2. Since the pump housing 16 located at the left has then been charged with a predetermined amount of abrasives such as sand, this pump housing will then be conditioned for discharge into the gathering chamber housing 42. Thus, when the air pressure within the pump housing 16 located at the left as viewed in FIG. 2, together with the combined weight of the abrasive therein is suflicient to overcome the air pressure in the gathering chamber, a mixture of sand and abrasive will be admitted to the gathering chamber from this pump housing. It will therefore be seen that a continuous supply of abrasive will be discharged from the device without the interruptions attendant with conventional systems. It will also be seen that since the hopper 12 is not a pressurized vessel the hopper may be loaded from time to time without necessitating an interruption or stoppage of the device.

From the foregoing description, it will be seen that I have provided a novel system for permitting flowable materials such as particulate abrasives to be continuously entrained in a stream of air for discharge against a selected surface to be treated.

It will be noted from the preceding paragraphs, that my novel system is arranged and constructed to permit gravity flow of the particulate flowable abrasive from an unpressurized source alternately into one of at least a pair of pump chambers wherein the flowable abrasive is pressurized and thereafter introduced into a gathering chamber for introduction into a discharge conduit associated with the surface treating apparatus. By alternately but continuously cycling the fiowable particulate abrasive through pressurized pump housings, the continuous air entrained stream of the abrasive may be discharged from the apparatus.

Thus, it will be seen that I have provided a novel and improved abrasive supply and conditioning system, which is not only of simple and inexpensive construction, but one which functions in a more efficient manner thanany heretofore known comparable systems.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the various parts without departing from the scope of my invention.

What I claim is:

1. Apparatus for continuously entraining a fiowable abrasive material into a stream of air, said apparatus comprising,

a supply receptacle for containing a supply of flowable abrasive, and having a material discharge means through which the abrasive material is discharged,

a pair of pressure chambers each having a material outlet and each having a material inlet for receiving material therethrough from the material discharge means of said supply receptacle,

each pressure chamber including a valve mechanism for opening and closing the material inlet and outlet thereof, each valve mechanism being operable in one cycle of operation to first open the material inlet and simultaneously close the material outlet of its associated pressure chamber to permit abrasive material to be introduced into the latter,

said valve mechanism for each chamber then closing each associated inlet to permit the pressure chamber to be pressurized to a predetermined pressure, and thereafter opening the material outlet to permit material to be discharged therefrom,

conduit means connected in communicating relation to said pressure chambers and being connected to a supply of air under pressure,

a gathering chamber structure connected to the source of air under pressure and having material receiving means interconnected with the material outlets of said pressure chambers for receiving the fiowable abrasive material and air therefrom,

said gathering chamber structure having material dispensing means through which a stream of air entrained fiowable abrasive materials is continuously discharged,

control mechanism interrelated with said valve mechanisms for continuously but alternately actuating said valve mechanisms with respect to each other through their respective cycles of operation whereby when one pressure chamber is being loaded with the flowable abrasive and thereafter pressurized, the other of said pressure chambers will simultaneously have its mixture of fiowable abrasive and air being discharged into the gathering chamber to thereby permit a continuous air entrained stream of abrasive to be produced.

2. The apparatus as defined in claim 1 wherein each of said valve mechanisms includes a pair of valve elements, one element of each pair being shiftable into and out of closing relation with the material inlet of the associated pressure chamber, and the other valve element of each pair being shiftable into and out of closing relation with respect to the material outlet of the associated pressure chamber, said valve elements being shiftable in response to a differential pressure acting upon opposed surfaces thereof.

3. Apparatus for continuously entraining a fiowable abrasive material into a stream of air,

said apparatus comprising a supply receptacle for containing a supply of fiowable particulate abrasive material, such as sand, and having a material discharge means through which the abrasive material is discharged,

a pair of pressure chambers each having a material outlet and each having a material inlet for receiving abrasive material therethrough from the material discharge means of said supply receptacle,

each pressure chamber having a pair of valve elements thereof shiftable into and out of closing relation with respect to said material inlet and outlet in response to a change in air pressure in the associated chamber,

each pair of valve elements being operable in one cycle of operation to first open the material inlet and simultaneously close the material outlet of its associated pressure chamber to permit abrasive material to be introduced into the pressure chamber, the material inlet then being closed by the associated valve element in response to fiuid pressure within the chamber while the material outlet of the pressure chamber is maintained in a closed condition to thereby permit the pressure chamber to be pressurized to a predetermined pressure, said material outlet valve element thereafter being shifted out of closing relation with respect to the material outlet of the pressure chamber to permit a mixture of air and abrasive to be discharged therefrom, conduit means connected in communicating relation to said pressure chambers and being connected to a supply of air under pressure,

a gathering chamber structure connected to a source of air under pressure and having a material receiving means connected in communicating relation with the material outlets of said pressure chambers for receiving the mixture of air and fiowable abrasive material therefrom,

said gathering chamber structure having material dispensing means through which a stream of air entrained fiowable abrasive material is discharged, control means including a pressure responsive control valve mechanism interposed in flow controlling relation with respect to said conduit means and being operable to alternately supply air under pressure to said pressure chambers and to exhaust air therefrom whereby when one of said pressure chambers is being loaded with an abrasive and thereafter pressurized, the other of said pressure chambers is discharging its mixture of air and abrasive into the gathering chamber to thereby permit a continuous air entrained stream of abrasive material to be discharged from the apparatus.

4. The apparatus as defined in claim 3 wherein said control means is connected in fluid communication with said pressure chambers and includes an actuating arm which is shiftable in response to a change in fluid pressure within said pressure chambers for engaging and actuating said control valve mechanism.

5. The apparatus as defined in claim 4 wherein said control means also comprises a fluid pressure cylinder and piston unit having a piston rod which is connected with said actuating arm.

6. The apparatus as defined in claim 3 wherein the interior of the supply receptacle is normally at atmospheric pressure.

7. The apparatus as defined in claim 6 wherein said material discharge means for said supply receptacle comprises a pair of discharge openings each connected in communicating relation with the material inlet of one of said pressure chambers and whereby abrasive material in the supply receptacle flows by action of gravity into the pressure chamber when the material inlet of the latter is in open condition.

8. The apparatus as defined in claim 4 wherein said gathering chamber structure is positioned below said pressure chamber so that the mixture of air and abrasive flow into the gathering chamber structure by action of gravity.

9. The apparatus as defined in claim 4 wherein said material dispensing means of said gathering chamber structure includes a metering valve mechanism which is connected to a source of air under pressure and through which a rapidly moving stream of air passes, said metering valve continuously introducing and entraining the abrasive into the rapidly moving stream of air for discharge therefrom.

10. A method of continuously entraining a fiowable abrasive material into a stream of air under pressure, said methodcomprising the steps of alternately intercommunicating each of a pair of'confined pressure zones with a supply of abrasive material, each pressure zone being in an unpressurized condition when interconnected with a supply of abrasive material to permit alternate loading of each pressure zone with the abrasive material, closing communication of each pressure zone with the supply of abrasive material when each pressure zone is loaded with the abrasive material and simultaneously pressurizing each loaded pressure zone with air under pressure, alternately intercommunicating each pressurized loaded pressure zone with a pressurized collection zone, the latter having a slightly lower air pressure than the pressure zone intercommunicated therewith whereby abrasive material flows from the loaded pressure zone into the collection zone so that when abrasive material in the loaded pressure zone is being evacuated into the collec tion zone, intercommunicating relation of the other pressure zone with the collection zone is closed and said other pressure zone is being supplied with abrasive material, continuously discharging the fiowable abrasive material from the collection zone and entraining the abrasive material in a rapidly moving stream of air under pressure.

References Cited UNITED STATES PATENTS 699,405 5/ 1902 Newhouse 51-12 2,443,148 6/ 1948 Rucki 51-12 3,266,193 8/1966 McCune 51-12 LESTER M. SWINGLE, Primary Examiner. 

